Heroin has become so pervasive in cities across America, and so profitable for the cartels that supply it that even cops admit the sporadic arrests they make have little effect. Cartels have begun lacing heroin with synthetic opioids including fentanyl, making a dose more addictive and cheaper to produce. Overdose reversal shots are helping addicts survive, often to use again, giving dealers a steady supply of repeat customers. With persistent demand and increasingly wide profit margins, 2017 is shaping up as the most profitable year ever for the U.S. heroin trade.